Thin film transistor, method of manufacturing the same and flat panel display device having the same

ABSTRACT

A thin film transistor (TFT) using an oxide semiconductor as an active layer, a method of manufacturing the TFT, and a flat panel display device having the TFT include source and drain electrodes formed on a substrate; an active layer formed of an oxide semiconductor disposed on the source and drain electrodes; a gate electrode; and an interfacial stability layer formed on at least one of top and bottom surfaces of the active layer. In the TFT, the interfacial stability layer is formed of an oxide having a band gap of 3.0 to 8.0 eV. Since the interfacial stability layer has the same characteristics as a gate insulating layer and a passivation layer, chemically high interface stability is maintained. Since the interfacial stability layer has a band gap equal to or greater than that of the active layer, charge trapping is physically prevented.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.13/091,614, filed on Apr. 21, 2011, which is a divisional of U.S.application Ser. No. 12/424,860, filed on Apr. 16, 2009, now U.S. Pat.No. 7,994,500, and claims priority from and the benefit of Korean PatentApplication No. 10-2008-0062417, filed on Jun. 30, 2008, all of whichare incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Aspects of the present invention relate to a thin film transistor usingan oxide semiconductor as an active layer, a method of manufacturing thesame and a flat panel display device having the same. More particularly,aspects of the present invention relate to a thin film transistor havingan interfacial stability layer formed on one surface or both surfaces ofan active layer, a method of manufacturing the same and a flat paneldisplay device having the same.

2. Description of the Related Art

In general, a thin film transistor (TFT) includes an active layerproviding channel, source and drain regions, and a gate electrode formedon the channel region and electrically isolated from the active layer bya gate insulating layer.

The active layer of the TFT configured as described above is generallyformed of a semiconductor material such as amorphous silicon orpoly-silicon. However, if the active layer is formed of amorphoussilicon, mobility is low, and therefore, it is difficult to operate adriving circuit at a high speed. If the active layer is formed ofpoly-silicon, mobility is high while a threshold voltage is not uniform.Therefore, a separate compensation circuit should be added.

Since a conventional method of manufacturing a TFT using low temperaturepoly-silicon (LTPS) involves a high-cost process such as laser heattreatment, equipment investment and management costs are high, and it isdifficult to apply the conventional method to a large-sized substrate.

In order to solve such a problem, studies on an oxide semiconductor usedas an active layer have recently been conducted.

A TFT using a zinc oxide (ZnO) or oxide semiconductor having ZnO as amain component as an active layer has been disclosed in JapaneseLaid-open Publication No. 2004-273614.

The oxide semiconductor having ZnO as a main component is estimated tobe a stable material because of its amorphous state and high mobility.If such an oxide semiconductor is used as an active layer, a TFT can bemanufactured using a conventional equipment without additionallypurchasing separate processing equipment. The oxide semiconductor isdeposited at a low temperature, and ion implantation is not required.Further, the oxide semiconductor is deposited using a sputtering method.Therefore, the oxide semiconductor can be applied to a large-sizedsubstrate.

However, since a TFT using an oxide semiconductor as an active layer haselectrical characteristics that are easily changed depending onstructures of the TFT and processing conditions, reliability may belowered. Particularly, when the TFT is driven by constant-voltage orconstant-current, a threshold voltage is changed in a positive (+)direction depending on time. It is estimated that such a phenomenon iscaused by charge trapping due to the deterioration of an interfacebetween an active layer and an insulating layer, or an active layer anda passivation layer.

SUMMARY OF THE INVENTION

Aspects of the present invention provide a thin film transistor (TFT)capable of improving interfacial characteristics of an active layer, amethod of manufacturing the same, and a flat panel display device havingthe same.

Aspects of the present invention provide a TFT capable of preventingcharge trapping in an interface of an active layer, a method ofmanufacturing the same, and a flat panel display device having the same.

Aspects of the present invention provide a TFT having high electricalcharacteristics and reliability, a method of manufacturing the same, anda flat panel display device having the same.

According to an aspect of the present invention, a TFT includes: asubstrate; source and drain electrodes formed on the substrate; anactive layer formed of an oxide semiconductor and formed to at leastpartially overlap both of the source and drain electrodes; a gateinsulating layer formed on the substrate to cover the active layer andthe source and drain electrodes; a gate electrode formed on the gateinsulating layer and insulated from the active layer by the gateinsulating layer; and an interfacial stability layer formed on one orboth of top and bottom surfaces of the active layer, wherein theinterfacial stability layer is formed of an oxide having a band gap of3.0 to 8.0 eV.

According to another aspect of the present invention, a method ofmanufacturing a TFT includes: forming source and drain electrodes on asubstrate; sequentially forming a first interfacial stability layer andan oxide semiconductor layer on the substrate having the source anddrain electrodes; patterning the oxide semiconductor layer, therebyforming an active layer; forming a gate insulating layer on thesubstrate having the active layer; and forming a gate electrode on thegate insulating layer formed above the active layer, wherein the firstinterfacial stability layer is formed of an oxide having a band gap of3.0 to 8.0 eV.

According to still another aspect of the present invention, a method ofmanufacturing a TFT includes: forming source and drain electrodes on asubstrate; sequentially forming an oxide semiconductor layer and aninterfacial stability layer on the substrate having the source and drainelectrodes; patterning the interfacial stability layer and the oxidesemiconductor layer, thereby forming an active layer; forming a gateinsulating layer on the substrate having the active layer; and forming agate electrode on the gate insulating layer above the active layer,wherein the interfacial stability layer is formed of an oxide having aband gap of 3.0 to 8.0 eV.

According to another aspect of the present invention, a flat paneldisplay device having a TFT includes: a first substrate having aplurality of pixels, a plurality of TFTs and a plurality of firstelectrodes formed thereon, the pixels being defined by a plurality offirst and second conductive lines, the TFTs controlling signals suppliedto the respective pixels, and the first electrodes being respectivelycoupled to the TFTs; a second substrate having a second electrode formedthereon; and a liquid crystal layer injected into a space sealed betweenthe first and second electrodes, wherein each of the TFTs includes:source and drain electrodes formed on the first substrate; an activelayer made of an oxide semiconductor and partially overlapped with thesource and drain electrodes; a gate electrode isolated from the activelayer by a gate insulating layer; and an interfacial stability layerformed on one or both of top and bottom surfaces of the active layer,wherein the interfacial stability layer is formed of an oxide having aband gap of 3.0 to 8.0 eV.

According to another aspect of the present invention, a flat paneldisplay device having a TFT includes: a first substrate having organiclight emitting devices and TFTs formed thereon, the organic lightemitting devices each including a first electrode, an organic thin filmlayer and a second electrode, and the TFTs controlling operations of therespective organic light emitting devices; and a second substratedisposed opposite to the first substrate, wherein each of the TFTsincludes: source and drain electrodes formed on the first substrate; anactive layer made of an oxide semiconductor and partially overlappedwith the source and drain electrodes; a gate electrode isolated from theactive layer by a gate insulating layer; and an interfacial stabilitylayer formed on one or both of top and bottom surfaces of the activelayer, wherein the interfacial stability layer is formed of an oxidehaving a band gap of 3.0 to 8.0 eV.

In a TFT according to aspects of the present invention, an interfacialstability layer is formed on one surface or both surfaces of an activelayer. Since the interfacial stability layer containing an oxide has thesame characteristic as a gate insulating layer and a passivation layer,chemically high interface stability is maintained. Since the interfacialstability layer has a band gap equal to or greater than that of theactive layer, charge trapping is physically prevented. Accordingly, achange in electrical characteristics such as a change in thresholdvoltage is minimized by the high interface stability and electric chargemobility, and it is possible to prevent reliability from being lowereddepending on temperature and time. When a TFT according to aspects ofthe present invention is applied to a flat panel display device,improved image quality can be implemented by stable electricalcharacteristics.

Additional aspects and/or advantages of the invention will be set forthin part in the description which follows and, in part, will be obviousfrom the description, or may be learned by practice of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects and advantages of the invention will becomeapparent and more readily appreciated from the following description ofthe embodiments, taken in conjunction with the accompanying drawings ofwhich:

FIG. 1 is a cross-sectional view of a thin film transistor (TFT)according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view of a TFT according to an embodiment ofthe present invention.

FIG. 3 is a cross-sectional view of a TFT according to an embodiment ofthe present invention.

FIGS. 4A to 4D are cross-sectional views illustrating a method ofmanufacturing a TFT according to aspects of the present invention.

FIGS. 5A and 5B are graphs showing reliability measurement results of aTFT according to aspects of the present invention.

FIGS. 6A to 6C are graphs showing stress measurement results of a TFTaccording to aspects of the present invention.

FIG. 7 is a perspective view showing an embodiment of a flat paneldisplay device having a TFT according to aspects of the presentinvention.

FIGS. 8A and 8B are respectively plan and cross-sectional views showinganother embodiment of a flat panel display device having a TFT accordingto aspects of the present invention.

FIG. 9 is a cross-section view of an organic light emitting device ofFIG. 8A.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Reference will now be made in detail to the present embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings, wherein like reference numerals refer to the like elementsthroughout. The embodiments are described below in order to explain thepresent invention by referring to the figures.

In the following detailed description, only certain exemplaryembodiments of the present invention have been shown and described,simply by way of illustration. As those skilled in the art wouldrealize, the described embodiments may be modified in various differentways, all without departing from the spirit or scope of the presentinvention. Accordingly, the drawings and description are to be regardedas illustrative in nature and not restrictive. In addition, when anelement is referred to as being “on,” “formed on,” or “disposed on”another element, it can be directly on, formed directly on, or disposeddirectly on the element or one or more intervening elements may bedisposed therebetween. Also, when an element is referred to as being“connected to,” “coupled to,” or “electrically coupled to” anotherelement, it can be directly connected to the element or be indirectlyconnected to the element with one or more intervening elementsinterposed therebetween. Hereinafter, like reference numerals refer tolike elements.

FIG. 1 is a cross-sectional view of a thin film transistor (TFT)according to an embodiment of the present invention, in which an exampleof the TFT having a top-gate structure is illustrated. A buffer layer 11is formed on a substrate 10, and source and drain electrodes 12 a and 12b are formed on the buffer layer 11. An active layer 13 made of an oxidesemiconductor and an interfacial stability layer 14 are sequentiallyformed on the substrate 10 having the source and drain electrodes 12 aand 12 b. A gate insulating layer 15 is formed on the substrate 10having the active layer 13, and a gate electrode 16 is formed on thegate insulating layer 15 above the active layer 13. Although not shown,the interfacial stability layer 14 may be formed wider than the activelayer 13.

FIG. 2 is a cross-sectional view of a TFT according to an embodiment ofthe present invention, in which another example of the TFT having atop-gate structure is illustrated. A buffer layer 21 is formed on asubstrate 20, and source and drain electrodes 22 a and 22 b are formedon the buffer layer 21. An interfacial stability layer 23 and an activelayer 24 made of an oxide semiconductor are sequentially formed on thesubstrate 20 having the source and drain electrodes 22 a and 22 b. Agate insulating layer 25 is formed on the substrate 20 having the activelayer 24, and a gate electrode 26 is formed on the gate insulating layer25 above the active layer 24. Although not shown, the interfacialstability layer 23 may be formed wider than the active layer 24.

FIG. 3 is a cross-sectional view of a TFT according to an embodiment ofthe present invention, in which still another example of the TFT havinga top-gate structure is illustrated. A buffer layer 31 is formed on asubstrate 30, and source and drain electrodes 32 a and 32 b are formedon the buffer layer 31. A first interfacial stability layer 33, anactive layer 34 made of an oxide semiconductor, and a second interfacialstability layer 35 are sequentially formed on the substrate 30 havingthe source and drain electrodes 32 a and 32 b. A gate insulating layer36 is formed on the substrate 30 having the active layer 34, and a gateelectrode 37 is formed on the gate insulating layer 36 above the activelayer 34. Although not shown, the first and/or second interfacialstability layers 33 and 35 may be formed wider than the active layer 34.

The active layer 13, 24, and 34 is disposed so that both side portionsof the active layer 13, 24, and 34 are partially overlapped with thesource and drain electrodes 12 a and 12 b, 22 a and 22 b, and 32 a and32 b, respectively. A channel region of the active layer 13, 24, and 34is overlapped with the gate electrode 16, 26, and 37. The oxidesemiconductor of the active layers 13, 24, and 34 comprise zinc oxide(ZnO) and be doped with at least one ion of gallium (Ga), indium (In),tin (Sn), zirconium (Zr), hafnium (Hf), cadmium (Cd), silver (Ag),copper (Cu), germanium (Ge), gadolinium (Gd), and vanadium (V). Forexample, each of the active layers 13, 24, and 34 may be formed of ZnO,ZnGaO, ZnInO, ZnSnO, GaInZnO, CdO, InO, GaO, SnO, AgO, CuO, GeO, GdO,HfO, or the like.

The interfacial stability layer 14, 23, 33, and 35 comprises an oxidehaving a band gap equal to or greater than that of the active layer 13,24 or 34, e.g., a band gap of 3.0 to 8.0 eV. The interfacial stabilitylayer 14, 23, 33, and 35 comprises any one selected from the groupconsisting of SiO_(x), SiO_(x)N_(y), SiO_(x)C_(y), SiO_(x)C_(y)H_(z),SiO_(x)F_(y), GeO_(x), GdO_(x), AlO_(x), GaO_(x), SbO, ZrO_(x), HfO_(x),TaO_(x), YO_(x), VO_(x), MgO_(x), CaO_(x), BaO_(x),SrO_(x), and spin onglass (SOG).

As shown in FIGS. 1 to 3, the interfacial stability layer 14, 23, 33,and 35 is formed on one surface or both surfaces of the active layer 13,24, and 34. Each of the interfacial stability layers 14, 23, 33, and 35is formed of an oxide having a band gap of 3.0 to 8.0 eV. If the bandgap of the interfacial stability layers 14, 23, 33, and 35 is smallerthan that of the active layers 13, 24, and 34, e.g., 3.0 eV, electriccharges are easily transferred, and therefore, carriers of the channelregion of the active layer 13, 24, and 34 cannot be effectively used. Ifthe band gap of the interfacial stability layer 14, 23, 33, and 35 isgreater than 8.0 eV, electrical characteristics are lowered due to ahigh insulation characteristic. Since the interfacial stability layer14, 23, 33, and 35 containing an oxide has the same characteristic asthe gate insulating layer 15, 25, and 36 and a passivation layer (notshown), chemically high interface stability is maintained. Since theinterfacial stability layers 14, 23, 33, and 35 have a band gap equal toor greater than that of the active layers 13, 24, and 34, chargetrapping is physically prevented.

In order to increase an effect of preventing charge trapping, the effect[H], [OH⁻] concentration of the interfacial stability layer 14, 23, 33,and 35 is preferably adjusted to be less than 10¹⁹/cm³. If the netelectron concentration of the interfacial stability layer 14, 23, 33,and 35 from the remnant [H], [OH⁻] is higher than 10¹⁹/cm³, hydrogen orhydroxyl atom/molecule/ion is penetrated (diffused) through a surface ofthe active layer 13, 24, and 34 to serve as a trap. For this reason,electrical characteristics of the active layer 13, 24, and 34 may belowered. In order to adjust the [H] or [OH⁻] concentration of theinterfacial stability layer 14, 23, 33, and 35 to be 10⁺¹⁹/cm³ or lower,a physical deposition method, such as a sputtering deposition method,may be used rather than a chemical deposition method.

Since the interfacial stability layer 14, 23, 33, and 35 protects achannel region of the active layer 13, 24, and 34 and increases a curingeffect in a subsequent heat treatment process, damage of the activelayer 13, 24, and 34 can be recovered.

Preferably, the interfacial stability layer 23 and 33 disposed betweenthe active layer 24 and 34, respectively, and the source and drainelectrodes 22 a and 22 b and 32 a and 32 b are formed to a thickness ofbelow 100 Å so that contact resistance between the active layer 13, 24,and 34 and the source and drain electrodes 22 a and 22 b and 32 a and 32b can be maintained to be low. More preferably the interfacial stabilitylayer 23 and 33 is formed to a thickness of 10 to 20 Å. Preferably, theinterfacial stability layer 14 and 35 formed on the top surface of theactive layer 13 and 34 is formed to have, for example, a thickness of 50to 5000 Å so as to sufficiently protect the active layer 13 and 34 andto maintain interface stability.

Hereinafter, a method of manufacturing a TFT configured as describedabove according to aspects of the present invention will be described indetail with reference to FIGS. 4A to 4D. For convenience ofillustration, the structure of FIG. 3 will be described as an example.

Referring to FIG. 4A, source and drain electrodes 32 a and 32 b areformed by forming a conductive layer on a substrate 30 using Mo, MoW,Al, AlNd, AlLiLa, or the like, and then patterning the conductive layer.A buffer layer 31 may be formed on the substrate 30 so as to preventdiffusion of impurities, and the source and drain electrodes 32 a and 32b may be formed on the buffer layer 31. The substrate 30 may include asemiconductor substrate such as silicon (Si), an insulative substrate,such as glass or plastic, or a metal substrate.

Referring to FIG. 4B, a first interfacial stability layer 33, an oxidesemiconductor layer 39, and a second interfacial stability layer 35 aresequentially formed on the substrate 30 having the source and drainelectrodes 32 a and 32 b. Each of the first and second interfacialstability layers 33 and 35 comprises an oxide having a band gap equal toor greater than that of the oxide semiconductor layer 39, e.g., a bandgap of 3.0 to 8.0 eV. Each of the first and second interfacial stabilitylayers 33 and 35 may include any one selected from the group consistingof SiO_(x), SiO_(x)N_(y), SiO_(x)C_(y), SiO_(x)C_(y)H_(z), SiO_(x)F_(y),GeO_(x), GdO_(x), AlO_(x), GaO_(x), SbO, ZrO_(x), HfO_(x), TaO_(x),YO_(x), VO_(x), MgO_(x), CaO_(x), BaO_(x), SrO_(x), and SOG.

A silicon oxide (SiO_(x)) or aluminum oxide (AlO_(x)) may be depositedusing a physical method, such as a radio frequency (RF) or a directcurrent (DC) sputtering deposition method. When an aluminum oxide(AlO_(x)) is deposited using the RF sputtering deposition method, anoxygen ratio is adjusted to be about 4 to 10%, thereby forming the firstand second interfacial stability layers 33 and 35 to have an excellentreliability against stresses, such as a temperature and a gate bias.

Referring to FIG. 4C, the oxide semiconductor layer 39 is formed into anactive layer 34 by sequentially patterning the second interfacialstability layer 35, the oxide semiconductor layer 39, and the firstinterfacial stability layer 33. At this time, the first interfacialstability layer 33 formed on the bottom surface of the oxidesemiconductor layer 39 may not be patterned, according to aspects of thepresent invention.

Referring to FIG. 4D, a gate insulating layer 36 is formed on thesubstrate 30 having the active layer 34, and the gate insulating layer36 is formed of SiO₂, SiN_(X), GaO₃, or the like. A gate electrode 37 isformed on the gate insulating layer 36 and formed above the active layer34 by forming a conductive layer on the gate insulating layer 36 usingAl, Cr, MoW, or the like, and then patterning the conductive layer.

FIG. 5A is a graph showing reliability measurement results of a TFTaccording to aspects of the present invention in which an interfacialstability layer is formed using an aluminum oxide (AlO_(x)). Because athreshold voltage (Vth), a s-factor (sub-threshold slop-factor), and anoff-current were hardly changed after a temperature was increased from aroom temperature to 100° C., the TFT has an excellent reliability. FIG.5B is a graph showing reliability measurement results of a TFT accordingto aspects of the present invention in which an interfacial stabilitylayer is formed by depositing a silicon oxide (SiO_(x)) using a plasmaenhanced chemical vapor deposition (PECVD). As a temperature increased,a threshold voltage (Vth) was changed in a negative direction, and aslop-factor was degraded.

FIGS. 6A and 6B are graphs showing stress measurement results of a TFTaccording to aspects of the present invention. In FIG. 6A, a voltageV_(GS) of 15V was applied to a gate electrode for 1 hour, and in FIG.6B, a voltage V_(GS) of −15V was applied to the gate electrode for 1hour. In FIG. 6A, the change in threshold voltage (Vth) was 0.5V, and inFIG. 6B, the change in threshold voltage (Vth) was 0.7V. FIG. 6C is agraph showing stress measurement results of a TFT according to aspectsof the present invention in which an interfacial stability layer isformed using a silicon oxide (SiO_(x)). The silicon oxide (SiO_(x)) isgenerally used in manufacturing a poly-silicon TFT, and a thermal oxide(SiO₂) formed at a temperature of 900° C. using a dry (O₂) or wet (H₂O)thermal oxidation method was used as the silicon oxide (SiO_(x)). When avoltage V_(GS) of 15V was applied to a gate electrode for 1 hour, thechange in threshold voltage (Vth) was 2.1V, and when a voltage V_(GS) of−15V was applied to the gate electrode for 1 hour, the change inthreshold voltage (Vth) was −2.8V. Therefore, it can be seen thatreliability of the TFT is remarkably improved as compared with theconventional TFT through the results of FIGS. 6A, 6B, and 6C.

A TFT according to aspects of the present invention may be applied to aflat panel display device. FIG. 7 is a perspective view showing anembodiment of a flat panel display device having a TFT according toaspects of the present invention. A display panel 100 displaying imageswill be schematically described.

The display panel 100 includes two substrates 110 and 120 disposedopposite to each other, and a liquid crystal layer 130 disposed betweenthe two substrates 110 and 120. In the display panel 100, pixel regions113 are defined by a plurality of gate and data lines 111 and 112 andare arranged in a matrix form.

A TFT 114 controls a signal supplied to each pixel and a pixel electrode115 coupled to the transistor 114 is formed at each of the intersectionportion of the gate and data lines 111 and 112 on the substrate 110. TheTFT 114 has any one of the structures of FIGS. 1 to 3, and may bemanufactured using the method of manufacturing a TFT, described withreference to FIGS. 4A to 4D.

A color filter 121 and a common electrode 122 are formed on thesubstrate 120. Polarizing plates 116 and 123 are formed at rear surfacesof the substrates 110 and 120, respectively, and a backlight (not shown)is disposed below a polarizing plate 116.

Meanwhile, a liquid crystal display (LCD) drive IC (not shown) drivingthe display panel 100 is mounted at a side of the pixel regions 113 ofthe display panel 100. The LCD drive IC converts electric signalsprovided from the outside of the display panel 100 into scan and datasignals, and then supplies the converted scan and data signals to thegate and data lines 111 and 112.

FIGS. 8A and 8B are respectively plan and cross-sectional views showinganother embodiment of a flat panel display device having a TFT accordingto aspects of the present invention. A display panel 200 displayingimages will be schematically described.

Referring to FIG. 8A, a substrate 210 is divided into a pixel region 220and a non-pixel region 230 surrounding the pixel region 220. A pluralityof organic light emitting devices 300 connected in a matrix form betweenscan and data lines 224 and 226 are formed on the substrate 210 of thepixel region 220. On the substrate 210 of the non-pixel region 230 areformed the scan and data lines 224 and 226 extended from the pixelregion 220, a power supply line (not shown) operates the organic lightemitting devices 300, and scan and data drivers 234 and 236,respectively, supply signals provided from the outside of the displaypanel 200 to the scan and data lines 224 and 226.

Referring to FIG. 9, the organic light emitting device 300 includes ananode electrode 317, a cathode electrode 320 and an organic thin filmlayer 319 formed between the anode and cathode electrodes 317 and 320.The organic thin film layer 319 is formed to have a structure in which ahole transfer layer, an organic light emitting layer and an electrontransfer layer are laminated. A hole injection layer, a hole blockinglayer, an electron blocking layer, and an electron injection layer maybe further included in the organic thin film layer 319. The organiclight emitting device 300 may further include a TFT to control anoperation of the organic light emitting device 300 and a capacitor tomaintain signals.

The TFT may have any one of the structures of FIGS. 1 to 3, and may bemanufactured using the method of manufacturing a TFT, described withreference to FIGS. 4A to 4D. Hereinafter, the organic light emittingdevice 300 including a TFT will be described in detail with reference toFIGS. 8A and 9.

A buffer layer is formed on the substrate 210, source and drainelectrodes 32 a and 32 b are formed on the buffer layer 31 in the pixelregion 220. At this time, a data line 226 coupled to one of the sourceand drain electrodes 32 a and 32 b are formed in the pixel region 220.The data line 226 may extend from the pixel region 220 and a pad 228 toreceive signals provided from the outside of the display panel 200, andmay be formed in the non-pixel region 230.

A first interfacial stability layer 33, an oxide semiconductor layer 39,and a second interfacial stability layer 35 are sequentially formed onthe substrate 210 having the source and drain electrodes 32 a and 32 b.The second interfacial stability layer 35 and the oxide semiconductorlayer 39 are patterned, sequentially or concurrently, thereby formingthe active layer 34. A gate insulating layer 36 is formed on thesubstrate 210 having the active layer 39, and a gate electrode 37 isformed on the gate insulating layer 36 and formed above the active layer39. At this time, a scan line 224 coupled to the gate electrode 37 isformed in the pixel region 220. The scan line 224 may be extended fromthe pixel region 220 and a pad 228 to receive signals provided from theoutside of the display panel 300 may be formed in the non-pixel region230.

A planarization layer 38 is formed above the thin film transistordescribed above, and a via hole is formed in the planarization layer 38and the gate insulating layer 36 so that the source or drain electrode32 a or 32 b is exposed. An anode electrode 317 is formed to be coupledto the source or drain electrode 32 a or 32 b through the via hole.

A pixel defining layer 318 is formed on the planarization layer 38 sothat a region (a light emitting region) of the anode electrode 317 isexposed, and an organic thin film layer 319 is formed on the exposedanode electrode 317. A cathode electrode 320 is formed on the pixeldefining layer 318 having the organic thin film layer 319.

Referring to FIG. 8B, a sealing substrate 400 sealing the pixel region220 is disposed above the substrate 210 having the organic lightemitting device 300, and the sealing substrate 400 is joined with thesubstrate 210 by a sealing member 410, thereby completing the displaypanel 200.

Although a few embodiments of the present invention have been shown anddescribed, it would be appreciated by those skilled in the art thatchanges may be made in this embodiment without departing from theprinciples and spirit of the invention, the scope of which is defined inthe claims and their equivalents.

What is claimed is:
 1. A flat panel display device, comprising: a firstsubstrate having disposed thereon: first and second conductive lines,the first conductive lines disposed to cross the second conductivelines, a plurality of pixels, each of the plurality of pixels having afirst electrode and being defined by the first and second conductivelines, and a plurality of thin film transistors electrically coupled tothe first electrodes to control signals supplied to the pixels,respectively; a second substrate having a second electrode formedthereon; and a liquid crystal layer disposed in a sealed space betweenthe first and second electrodes, wherein each of the thin filmtransistors comprises: source and drain electrodes formed on the firstsubstrate, one of the source and drain electrodes electrically coupledto one of the first and second conductive lines, and the other of thesource and drain electrodes electrically coupled to the first electrode,an active layer formed of an oxide semiconductor and formed to at leastpartially overlap both the source and drain electrodes, a gateinsulating layer formed on the first substrate to cover the active layerand the source and drain electrodes, a gate electrode formed on the gateinsulating layer and insulated from the active layer by the gateinsulating layer, the gate electrode electrically connected to the otherof the first and second conductive lines, and an interfacial stabilitylayer formed on at least one of top and bottom surfaces of the activelayer, the interfacial stability layer being formed of an oxide having aband gap of 3.0 to 8.0 eV, wherein a portion of the interfacialstability layer is disposed between the source and drain electrodes andthe active layer.
 2. The flat panel display device of claim 1, whereinthe oxide semiconductor comprises zinc oxide (ZnO).
 3. The flat paneldisplay device of claim 2, wherein the oxide semiconductor is doped withat least one ion of gallium (Ga), indium (In), tin (Sn), zirconium (Zr),hafnium (Hf), cadmium (Cd), silver (Ag), copper (Cu), germanium (Ge),gadolinium (Gd), and vanadium (V).
 4. The flat panel display device ofclaim 1, wherein the interfacial stability layer comprises one selectedfrom the group consisting of SiO_(x), SiO_(x)N_(y), SiO_(x)C_(y),SiO_(x)C_(y)H_(z), SiO_(x)F_(y), GeO_(x), GdO_(x), AlO_(x), GaO_(x),SbO, ZrO_(x), HfO_(x), TaO_(x), YO_(x), VO_(x), MgO_(x), CaO_(x),BaO_(x), SrO_(x), and SOG.
 5. A flat panel display device, comprising: afirst substrate having an organic light emitting device, gate and datalines, and a thin film transistor formed thereon, the organic lightemitting device including a first electrode, an organic thin film layer,and a second electrode, and the thin film transistor controllingoperation of the organic light emitting device; and a second substratedisposed opposite to the first substrate, wherein the thin filmtransistor comprises: source and drain electrodes formed on the firstsubstrate, one of the source and drain electrodes electrically connectedto one of the data lines, an active layer formed of an oxidesemiconductor and formed to at least partially overlap both the sourceand drain electrodes, a gate insulating layer formed on the substrate tocover the active layer and the source and drain electrodes, a gateelectrode formed on the gate insulating layer and insulated from theactive layer by the gate insulating layer, the gate electrodeelectrically connected to one of the gate lines, and an interfacialstability layer formed on at least one of top and bottom surfaces of theactive layer, the interfacial stability layer being formed of an oxidehaving a band gap of 3.0 to 8.0 eV, wherein a portion of the interfacialstability layer is disposed between the source and drain electrodes andthe active layer.
 6. The flat panel display device of claim 5, whereinthe oxide semiconductor comprises zinc oxide (ZnO).
 7. The flat paneldisplay device of claim 6, wherein the oxide semiconductor is doped withat least one ion of gallium (Ga), indium (In), tin (Sn), zirconium (Zr),hafnium (Hf), cadmium (Cd), silver (Ag), copper (Cu), germanium (Ge),gadolinium (Gd), and vanadium (V).
 8. The flat panel display device ofclaim 5, wherein the interfacial stability layer comprises one selectedfrom the group consisting of SiO_(x), SiO_(x)N_(y), SiO_(x)C_(y),SiO_(x)C_(y)H_(z), SiO_(x)F_(y), GeO_(x), GdO_(x), AlO_(x), GaO_(x),SbO, ZrO_(x), HfO_(x), TaO_(x), YO_(x), VO_(x), MgO_(x), CaO_(x),BaO_(x), SrO_(x), and SOG.